In U.S. Pat. Nos. 4,508,858 and 4,559,202 a method and apparatus are disclosed for continuously preparing aqueous polymer solutions such as partially hydrolyzed polyacrylamides. The apparatus includes a reactant-receiving vessel in which polymerization is initiated, a reactor in which polymerization is completed and a post-polymerization reactor or hydrolyzer in which polymer from the reactor is converted to the desired form. The initial reaction temperature is stated to be in the range of about 100.degree. F. to 110.degree. F. When polymerization has reached completion the polymer solution is withdrawn from the reactor and directed through a static mixer where it is mixed under continuous flow conditions with hydrolyzing agents, after which the mixture continues to the hydrolyzer. Although the patents are silent on the final polymerization temperatures, a final polymer temperature in the order of 135.degree. F. could be expected when the initial temperature is 105.degree. F.
It is now possible to carry out polymerization at higher temperatures than those disclosed in the U.S. Patents referred to above. This increases the polymer throughput, thus reducing plant costs. For example, initial and final temperatures of about 140.degree. F. and 190.degree. F., respectively, have been employed. While such temperatures permit the benefits mentioned, they also make the polymer susceptible to degradation in the context of a residence time of more than one or two days. Significant degradation can be avoided by operating with short residence times, but this would restrict operational flexibility and fail to make use of the desired storage capacity of the hydrolyzer.
It would be economically beneficial to be able to operate at the higher polymerization temperatures which have now become possible without, however, having to compensate by employing significantly shorter periods of residency in order to avoid degradation due to the high temperatures.